Need tuning help on 340

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midnight340

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Hi Guys, this is a long post, but I need some help understanding what I'm dealing with in tuning my 340. I installed an AEM wide-band and have been watching the plugs. At the end of the info I'll add photos of plugs.

This is a converted race motor with low compression (8.5 pistons) X heads ported to the max, port matched LD340, port matched 1-5/8" mid-length headers, and a Lunati 284 Bracket Master (.218 @ .050 and .458" lift. (I've run 13.95 @ 96 mph, vehicle wt. 3450 w/ driver)

To get reasonable A/F #'s I've had to jet the Edelbrock 750 8% lean to .107 primaries (stock .113) and 4% fat .110's in the secondaries (stock .107) and use a rod that is a combo of the largest size made for cruise and the smallest size made for power. (75/37 rod) A/F about 13.5 idle and cruise, mid rpm 14-15, and WOT 11.5-12.5 range.

This jetting seemed unusual. And I'd read to NEVER jet the secondaries larger than the primaries!

The motor loves a lot of initial advance (happy at 24), but so far I can't run more than 33-34 total without evidence of detonation. (MSD distr. through a 6A box limited to 15* mechanical with home-made bushing.) So my timing now is about 17-32. (vac. adv. not hooked up)

Besides plug choice, the motor runs great at lower rpms, good response, pulls good WOT, but seems to be done at 5,000 and it used to pull good to 6,500 and happily pass 7,000. (good oiling mods) Also Holley red through 3/8" pumps a gallon in 40 sec.

So why does it no longer have the top end? And how do the plugs look to you? And is the detonation due to hot plugs? (saw silver flecks on porcelin at 36*, yikes)

Re plugs, Autolite 63's were looking very hot. I just switched to NGK BP8ES, put fresh plugs in #1 and #7 cylinders and made a WOT run, shut it down and coasted to a stop. Both were similar, Here are the photos:
 

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Hi Guys, this is a long post, but I need some help understanding what I'm dealing with in tuning my 340. I installed an AEM wide-band and have been watching the plugs. At the end of the info I'll add photos of plugs.

This is a converted race motor with low compression (8.5 pistons) X heads ported to the max, port matched LD340, port matched 1-5/8" mid-length headers, and a Lunati 284 Bracket Master (.218 @ .050 and .458" lift. (I've run 13.95 @ 96 mph, vehicle wt. 3450 w/ driver)

To get reasonable A/F #'s I've had to jet the Edelbrock 750 8% lean to .107 primaries (stock .113) and 4% fat .110's in the secondaries (stock .107) and use a rod that is a combo of the largest size made for cruise and the smallest size made for power. (75/37 rod) A/F about 13.5 idle and cruise, mid rpm 14-15, and WOT 11.5-12.5 range.

This jetting seemed unusual. And I'd read to NEVER jet the secondaries larger than the primaries!

The motor loves a lot of initial advance (happy at 24), but so far I can't run more than 33-34 total without evidence of detonation. (MSD distr. through a 6A box limited to 15* mechanical with home-made bushing.) So my timing now is about 17-32. (vac. adv. not hooked up)

Besides plug choice, the motor runs great at lower rpms, good response, pulls good WOT, but seems to be done at 5,000 and it used to pull good to 6,500 and happily pass 7,000. (good oiling mods) Also Holley red through 3/8" pumps a gallon in 40 sec.

So why does it no longer have the top end? And how do the plugs look to you? And is the detonation due to hot plugs? (saw silver flecks on porcelin at 36*, yikes)

Re plugs, Autolite 63's were looking very hot. I just switched to NGK BP8ES, put fresh plugs in #1 and #7 cylinders and made a WOT run, shut it down and coasted to a stop. Both were similar, Here are the photos:

That red pump is damn near useless in some cases and would at least step it up to a blue or black. Do you run a pre-filter and how many microns is it...............Taking over the world one carb at a time....ThumperCarbs..............
 
I've wondered about that pump. It is new-ish, the pre-filter is a 10" oval track style with stainless mesh, I think 10 micron. Tank is new. Then a second small 70 micron (?) before the carb. Checked it and it's clean. I have a bypass regulator, but my gauge may not be reading right as it's inexpensive.
 
I have a 10* bushing so the engine gets the initial timing it wants.
 
The experts are often wrong. Your performance, wide band and plugs indicate lean on top end. As suggested I would verify fuel supply first then fatten it up if no issues with supply are found.
 
And what A/F ratio should I be seeing at the top end of a WOT run?

I usually read 12:1 is good, though this motor seems to like more fuel than any of the normally published guidelines.
 
I've wondered about that pump. It is new-ish, the pre-filter is a 10" oval track style with stainless mesh, I think 10 micron. Tank is new. Then a second small 70 micron (?) before the carb. Checked it and it's clean. I have a bypass regulator, but my gauge may not be reading right as it's inexpensive.

The filters are backwards..............the bigger goes BEFORE the pump and the smaller after.............Taking over the world one carb at a time..........ThumperCarbs...........
 
I've just go a relatively inexpensive timing light (non-dialback, which is recommended with MSD) Could be it is off.

And I'm not very experienced with reading plugs. I'd like opinions on the plug heat range, and any info as to timing that can be seen by you guys with more experience.

I could see no evidence of grey or tan at the base of the porcelain (with otoscope) in spite of what I'm told is a fairly fat A/F of about 11.5-12:1. (most sites say 12.5-13 it seems)
 
I've just go a relatively inexpensive timing light (non-dialback, which is recommended with MSD) Could be it is off.

And I'm not very experienced with reading plugs. I'd like opinions on the plug heat range, and any info as to timing that can be seen by you guys with more experience.

I could see no evidence of grey or tan at the base of the porcelain (with otoscope) in spite of what I'm told is a fairly fat A/F of about 11.5-12:1. (most sites say 12.5-13 it seems)

An 8 is a fairly cold plug and I run/race those in my 12.1.1 comp. n/a 9-second 470 BB..................Taking over the world one carb at a time........ThumperCarbs........
 
The filters are backwards..............the bigger goes BEFORE the pump and the smaller after.............Taking on the world one carb at a time..........ThumperCarbs...........

The filters aren't backwards, my brain was!!!!! Sorry about that. Just checked, I think the large pre-filter is 45 micron (Speedway motors) and the smaller before carb is a Summit 10 micron.
 
I've just go a relatively inexpensive timing light (non-dialback, which is recommended with MSD) Could be it is off.

And I'm not very experienced with reading plugs. I'd like opinions on the plug heat range, and any info as to timing that can be seen by you guys with more experience.

I could see no evidence of grey or tan at the base of the porcelain (with otoscope) in spite of what I'm told is a fairly fat A/F of about 11.5-12:1. (most sites say 12.5-13 it seems)

do you have a friend with a timing light?
also, are you sure you're getting all the way to the end of the advance curve when you are checking total timing? maybe there is a stiff second spring in the dist. that is extending the curve further up in the rpm range...

anyways, if i were you i would try to bump timing down a little lower even, maybe 2* more and see if it still detonates.

the plugs to look really clean too, but for full throttle you should be looking way down into the porcelain to see if you can see any color down there after a full throttle blast like you did...

once you get some color on the plug then maybe try adding a little more timing back in...
 
I'm not seeing detonation where it now is. I'm down about 3-4* from when it was.

Timing for total I've revved quite a ways past where the timing stopped advancing to get a reading.
(I have balancer that is degreed all the way around, and I have checked accuracy against TDC with a dial indicator.)

But I can't see any color at the base of the porcelain. (with LED otoscope) So I need to fatten the secondaries another step. (I guess what messes with my mind, is that the motor would want 2 steps lean in primaries from Edelbrock's "stock" and 2-3 steps rich in secondaries!)

As to plug temperature, I've run the Autolite 63's for a good bit of testing and see about 4 threads darkened, meaning I'm hot on the plug? The BP8ES plugs should be 2 steps colder so I'm thinking they should be OK to run for now?
 
what kind of pressure do you have in the cylinders over 180 psi? what type of fuel? a lot of old cylinders heads have been milled a lot ,mine were 53cc on my x heads , may be compression higher then you think and that's a small ,near stock cam spec, could cam be over advanced limiting top end and causing heat with late exhaust timing?
 
Haven't found the cam card yet, but I believe I installed it 4* advanced.
Cylinder pressure (hot, carb open) is a consistent 160#.
 
It seems to me, if you can get the AFRs down at 12, your fuel system is keeping up.
The 160PSI is indicating a good Dcr, which the 218*cam is trying to achieve.
At 3450, 96 mph is pretty good for an LC 340 with a tiny 218 cam.
If your power-timing is down at 32* or less, to avoid detonation, that is hurting your mph.
What your tach at,crossing the line, and in what gear are you. That makes quite a difference.With a 218 cam you probably want to be trapping at 5400?Or less even. If you are winding it out too far, that could really be hurting you too..

But really , you need to figure out why 32* is detonating.
Are you running oxiginated gas?And what grade?

Heat is the number 1 cause of detonation.Or rather too much of it, in the chamber. Low Compression, open chamber heads, also have trouble with pressure spiking too early.

Ok something is not right here;
I plugged some numbers into the Wallace calculator,and I can't make the numbers come out with your inputs. This is what you supplied; 160psi, 218 cam,8.5 Scr.. No matter how I fudge the numbers, I can't make the 160 psi.
Can you be a little more specific as to the cam? What I need is the ICA; Intake Closing Angle, or an advertised intake duration plus I need the LDA;Lobe Displacement Angle.Then are you absolutely sure the cylinder pressure is 160psi, and that the 8.5Scr is accurate?
Sorry, I could not find the "BracketMaster on the Lunati Website.

I did manage to make it work with 10.5 SCr, a 66*ICA, and got about 165psi. This would be a 284/108 cam in at 104*. But the .050 on a 284 cam is more like 236 to 240;no where near 218*.In any case, this yields a Dcr of 8.23 which as you have discovered is too much for pump gas, and iron heads.
 
First off, a 63 is not a hot plug for that compression ratio. As thumperdart said, that NGK is even colder. You don't want that.

I agree with Dom (thumperdart) you need to look at your fuel system.
 
with that cam having 218@ .050 and advanced 4deg its range will be reduced by 300rpm making the top power around 5200rpm do you know the lca of the cam. this could lower the range again.
 
Lunati at the time said 1800-5800 and I installed at their recommended advance.

But as I said, the motor has always happily revved way past that. Has seen 7,000 many times, but I usually shift at 6200-6500. I don't run at the strip but a few times a year, so am no expert at any of this. It just started feeling dead at the top end as I've gotten the A/F #'s "where they told me they should be" and unless I'm missing something the motor apparently does not agree.

I'm heading out now to have a good shop put their timing light on it to see if mine is off. And I am not sure how to check if I'm getting enough fuel pressure at the top end. Maybe I do need to rejet back to richer mix.
 
I run fuel pressure gauge on the cowl panel....Not always pretty for a street car but very informative...
 
A 45 micron is a bit small as a pre-filter. I never run anything smaller than a 100 micron before the pump.

Don't get caught up in A/F numbers. If you can get to a track, tune it by best MPH. The ranges can and will be all over the place depending on race fuel or pump gas. Pump gas with ehtanol will want a richer number than straight (race) gasoline. Not unusual to be in the low 12's and high 11's with a heavier ethanol blend.
 
I really appreciate all the response. And welcome any thoughts. I'm likely not too far off.

Tomorrow will check fuel pressure if I have to tape a gauge to the windshield.
(I am running 89 or 91 octane with no ethanol, so the pump says)

The only disadvantage to cold plugs is that I risk fouling, right? (But sure don't see any hint of that with the MSD box, even when I was at a much richer mix.)
 
The filters aren't backwards, my brain was!!!!! Sorry about that. Just checked, I think the large pre-filter is 45 micron (Speedway motors) and the smaller before carb is a Summit 10 micron.

You need a bigger pre filter than a 45 in my opinion and hopefully they`re not screen filters but sintered...............Taking over the world one carb at a time...........ThumperCarbs...........
 
I run fuel pressure gauge on the cowl panel....Not always pretty for a street car but very informative...



This thing is lean..... My last ownership of an A Body in the late 80's had a nice small block in it and I really struggled with making decent time slips.... The fuel pressure gauge on the Cowl was a turning point for me when I installed it. Details I don't remember so much but not too long after that I had 11 second time slips.... It is worth having one even if only temporary....

JW
 
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